syms a b x y;
[x0, y0, params, conditions] =solve(x==50*cos(a)+40*cos(a+b-pi),y==50*sin(a)+40*sin(a+b-pi),a>0,a<pi/2,b>pi/2,  b<pi,  [a,b], 'ReturnConditions', true);

syms x1 x2 x3 x4
[x1,x2,x3,x4,params,conditions] = solve(9*x1-3*x2-2*x3-3*x4==0,9*x2-5*x1-2*x3-3*x4==0,10*x3-2*x1-5*x2-3*x4==0,9*x4-2*x1-x2-6*x3==0,x1>=50,x1<=70,x2>=50,x2<=70,x3>=50,x3<=70,x4>=50,x4<=70,[x1,x2,x3,x4],'ReturnConditions',true)
solutions = [x1,x2,x3,x4];